1. The Field of the Invention
The present invention relates to the manufacture of nanometer-sized particles. More particularly, the present invention relates to methods for manufacturing highly dispersed nanoparticles from catalyst atoms that are caged between (e.g., complexed with) three or more ligands per catalyst atom.
2. Related Technology
Particle catalysts are an important component of many industrial applications such as refining, organic synthesis, fine chemicals manufacturing, and many other industrial processes. In many catalyzed reactions, improving catalyst performance has the potential to greatly improve the profitability and or viability of an industrial process. In many cases, a precious metal is used as the catalyst. By improving the catalyst performance, costs can be reduced because the amount of catalyst being used can be reduced and/or the amount of product being produced increases.
Improved catalyst performance has typically been achieved by reducing the size of the catalyst particles. Particulate catalysts are only active at the surface. Reducing the size of the catalyst particles increases the surface to weight ratio, thereby increasing catalyst performance. Recent improvements in techniques for manufacturing particle catalysts have enabled formation of nanoparticles having an average size of less than 5.0 nm. Even at these extremely small sizes, there is still a significant amount of metal that is not exposed on the outer surface, resulting in low metal utilization. For example, 2.5 nm platinum particles in a face centered cubic (“fcc”) crystal structure utilizes about 45% of the platinum atoms, whereas a 5.0 nm particle utilizes only about 23% of the platinum atoms. Therefore, to reach nearly atomic dispersion, the average particle size of the metal needs to be 2.5 nm or less, typically 1.5 nm or less.
One problem with making and maintaining particles less than 2.5 nm is particle stability. Particle stability is known to depend on particle surface area. As the surface area increases, the particle surface energy also increases, which can cause agglomeration of the catalyst particles. At particle sizes of 2.5 nm or less the surface energy is very high and catalyst made using existing methods agglomerate to form lager particles.